This invention relates to windshield wiper assemblies for automobiles and the like, and more particularly, to an improved wiper assembly which provides a better pivoting action than prior art devices.
A typical problem for windshield wipers is the failure of the wiper to flip from side to side when reversing the direction of motion. Consequently, the wiper element is forced along the windshield in an unpredictable manner often resulting in chatter or the like, but in any event, not providing the proper cleaning action. Such failure to flip is caused by many different factors including for example, the set of the wiper element or other aging characteristics, the strength of the spring holding the assembly against the glass, and the friction characteristics at the glass wiper interface. Still further factors include the curvature of the windshield, the force applying design of the superstructure portion of the wiper blade and the requirement inherent in many prior art designs that the wiper element flex throughout its length and lift the wiper superstructure against the force of the wiper spring. It is with this last parameter that the instant invention is primarily concerned.
Conventional wiper designs make use of a wiper section which is hinged in one of two manners. In each of these cases there is a main body of the wiper which flips at the end of a stroke. The flipping action is brought about by the change in direction at the end of a stroke and the fact that the friction coefficient is high enough to provide a horizontal force which acts on the strut shaped wiper body to cause it to flip over center.
One of these designs makes use of a hinge comprised of the rubber body section which rotates in the slot of the backing strip. This type of hinge has limited elastic properties and may be described as a "pivoted" hinge. Another popular type of hinge consists of a thin connecting strip of rubber which connects the body portion of the wiper to a base portion which in turn is attached to the backing strip. Here the flipping action occurs by the rotation of the body portion, using the thin connecting strip as a hinge. The thickness of this hinge is not so small that it has negligible bending resistance. It has a reasonable thickness and acts as an elastic member which bends to accomplish the flip but also attempts to restore itself to its straight unstressed position. This type of action can be referred to as an "elastic" hinge since it stores energy in being bent in one direction. This energy is released to assist the return to a center position prior to being flipped into the new reversed direction.
Since both of these designs depend upon the wiper body acting as a strut, both require a certain minimum friction between wiper and windshield in order to get the body portion to rise during reversal and then fall off toward the opposite side. As noted, a major problem with getting this to happen is that the wiper body shape becomes distorted with time. In part, this distortion occurs because of the downward pressure of the wiper arm which bends the lip and holds it bent over a period of months, causing a set in the rubber material and a permanently bent shape of the lip. This bend changes the angle that the strut makes with the windshield. When this angle becomes low enough the available friction is no longer sufficient force to raise the frame and bring the wiper body into the over center position.